Colourless Powdered Glass as an Additive in Fifteenth- and Sixteenth-Century European Paintings

Selection of data presented in support of the Spring article from Technical Bulletin Volume 33.

Additional information

Table 1: Fifteenth- and sixteenth-century paintings in which colourless powdered glass has been identified in paint samples, together with quantitative SEM–EDX analysis of the particles, normalised and expressed as weight % oxide (not including elements present at values lower than 0.1%). Updates since publication of the article appear in green.

School

Date Range

Artist, painting title, date and locationf

Areas where powdered glass was found and estimated particle size

glass type

Na2O

MgO

Al2O3

SiO2

P2O5e

SO3

Cl

K2O

CaO

TiO2

MnO

FeO

French

1498-1502

Master of Moulins (Jean Hey), Charlemagne, and the meeting of Saints Joachim and Anne at the Golden Gate (NG 4092), c.1500.

Off white priming, with a little lead white; black background, with coal black and a little verdigris; underpaint of marbled ledge, with lead white, a little red lake and brown; purple cloak of figure at the right, with red lake and a little lead white in the upper layer and with coal black, a little red lake, vermilion and lead-tin yellow in underpaint, 10–30 µmb

Off white priming, with a little lead white; Virgin’s red dress, with red lake; grey sword, with lead white and galena (lead sulphide); grey of architecture, with lead white and bone black; Saint John’s red cloak, with red lake and azurite, 10–30 µmb

Pale yellow priming, with lead white and a little lead-tin yellow; grey hose of figure fourth from the left, with lead white and coal black; red of cloak of figure second from the left, with red lake and vermilion; brownish-green foreground, with lead white, lead-tin yellow and a little azurite and verdigris, two types of glass, 10–20 µma

Pale yellow priming, with lead white and a little lead-tin yellow; grey hose of figure fourth from the left, with lead white and coal black; red of cloak of figure second from the left, with red lake and vermilion; brownish-green foreground, with lead white, lead-tin yellow and a little azurite and verdigris, two types of glass, 10–20 µma

Pale yellow priming, with lead white and a little lead-tin yellow; Saint John’s red drapery, with red lake; golden sun ray, with orpiment and a little lead-tin yellow; brown shadow of the drapery of the angel in yellow, with black, vermilion, red earth and red lake, 10–30 µma

soda ash

10.4

3.4

1.0

69.9

0.2

0.3

0.9

2.2

10.7

0.0

0.5

0.4

Italian

1505

Raphael, The Madonna and Child with Saint John the Baptist and Saint Nicholas of Bari (The Ansidei Madonna) (NG 1171), 1505, Umbria or Florence.

Pale yellow priming, with lead white and a little lead-tin yellow; dark purple underside of the canopy over the throne, with red lake, a little vermilion and black; Saint John’s red drapery, with red lake; pale grey architecture, with lead white and bismuth metal powder; mordant for the gilded decoration on the throne (used alone); yellow ‘wood’ on the throne, with lead-tin yellow and a little red earth, two types of glass, 10–20 µma

soda ash; high Al (sand)

11.8

2.4

5.0h

63.6

0.5

1.0

1.2

3.5

8.1

0.2

1.6

1.0

Italian

1505

Raphael, The Madonna and Child with Saint John the Baptist and Saint Nicholas of Bari (The Ansidei Madonna) (NG 1171), 1505, Umbria or Florence.

Pale yellow priming, with lead white and a little lead-tin yellow; dark purple underside of the canopy over the throne, with red lake, a little vermilion and black; Saint John’s red drapery, with red lake; pale grey architecture, with lead white and bismuth metal powder; mordant for the gilded decoration on the throne (used alone); yellow ‘wood’ on the throne, with lead-tin yellow and a little red earth, two types of glass, 10–20 µma

soda ash; low Al (pebbles)

10.9

3.2

1.5

66.6

0.2

1.4d

0.0

2.4

10.4

0.1

1.0

0.5

Italian

1507-1512

Raphael, The Madonna and Child with the Infant Baptist (The Garvagh Madonna) (NG 744), c.1509–10.

Shadow of red robe of man at right, with red lake (lower glaze layers only, and not final blotted glaze), c.10–20 µma

wood ash–lime (high lime–low potash)

1.5

3.1

4.0

61.0

3.0

0.7

0.5

5.4

19.0

0.3

0.9

0.7

Spanish

1565-1570

Luis de Morales, The Virgin and Child (NG 1229), probably 1565–70.

Red of Virgin’s dress, with red lake and a little lead white, 5–7 µma

soda ash, some particles leached

11.5

3.5

2.3

67.5

0.5

2.7d

1.4

3.5

5.8

0.1

0.7

0.6

a. Analysis carried out on carbon-coated samples under high vacuum conditions, 200 pA, 25 kV, 60s livetime.b. Analysis carried out on uncoated samples under variable pressure conditions, 200 pA, 25 kV, 60s livetime, 50 Pa, air as the chamber gas.c. Particles that seem to be a pure form of silica, containing only small amounts of other elements, were also detected in this sample.d. The apparent elevated sulphur concentration in this sample is probably not reliable and likely to result either from a sulphur-containing red lake pigment or, due to overlap of the sulphur peak with that from lead, a contribution to the spectrum from lead pigments around the glass.e. Red lake pigments, especially those based on insect dyestuffs, often contain phosphorus. This could contribute to the apparent concentration in the glass, especially where the particles are small.f. The binding medium of many of these paintings has been analysed by Gas Chromatography–Mass Spectrometry and identified as a drying oil. These analyses have generally been published in past issues of the National Gallery Technical Bulletin.g. In this sample the glass particles are very small and are embedded in a matrix of red lake, with a substrate containing alumina. The interaction volume of the electron beam is likely to be larger than the glass particle and the apparent aluminium concentration too high.h. The quantitative results quoted are from a particle in the priming layer, which does not contain red lake, or from a large particle in red lake paint; the high reported Al content is therefore reliable.i. A dispersion of a paint sample allowed individual glass particles to be seen in transmitted light under the microscope. They could be seen to have angular edges and showed conchoidal fracture, confirming that they were glass, despite the rather low alkali content seen by EDX analysis, which is a result of severe leaching. See the Appendix in J. Dunkerton and H. Howard, ‘Sebastiano del Piombo’s Raising of Lazarus: A History of Change’, National Gallery Technical Bulletin, 30, 2009, pp. 26–51.j. Details updated after publication, 2012.

:

School

Artist, painting title, date and locationf

Areas where powdered glass was found and estimated particle size

glass type

Na2O

MgO

Al2O3

SiO2

P2O5e

SO3

Cl

K2O

CaO

TiO2

MnO

FeO

French

Master of Moulins (Jean Hey), Charlemagne, and the meeting of Saints Joachim and Anne at the Golden Gate (NG 4092), c.1500.

Off white priming, with a little lead white; black background, with coal black and a little verdigris; underpaint of marbled ledge, with lead white, a little red lake and brown; purple cloak of figure at the right, with red lake and a little lead white in the upper layer and with coal black, a little red lake, vermilion and lead-tin yellow in underpaint, 10–30 µmb

Off white priming, with a little lead white; Virgin’s red dress, with red lake; grey sword, with lead white and galena (lead sulphide); grey of architecture, with lead white and bone black; Saint John’s red cloak, with red lake and azurite, 10–30 µmb

Pale yellow priming, with lead white and a little lead-tin yellow; grey hose of figure fourth from the left, with lead white and coal black; red of cloak of figure second from the left, with red lake and vermilion; brownish-green foreground, with lead white, lead-tin yellow and a little azurite and verdigris, two types of glass, 10–20 µma

Pale yellow priming, with lead white and a little lead-tin yellow; grey hose of figure fourth from the left, with lead white and coal black; red of cloak of figure second from the left, with red lake and vermilion; brownish-green foreground, with lead white, lead-tin yellow and a little azurite and verdigris, two types of glass, 10–20 µma

Pale yellow priming, with lead white and a little lead-tin yellow; Saint John’s red drapery, with red lake; golden sun ray, with orpiment and a little lead-tin yellow; brown shadow of the drapery of the angel in yellow, with black, vermilion, red earth and red lake, 10–30 µma

soda ash

10.4

3.4

1.0

69.9

0.2

0.3

0.9

2.2

10.7

0.0

0.5

0.4

Italian

Raphael, The Madonna and Child with Saint John the Baptist and Saint Nicholas of Bari (The Ansidei Madonna) (NG 1171), 1505, Umbria or Florence.

Pale yellow priming, with lead white and a little lead-tin yellow; dark purple underside of the canopy over the throne, with red lake, a little vermilion and black; Saint John’s red drapery, with red lake; pale grey architecture, with lead white and bismuth metal powder; mordant for the gilded decoration on the throne (used alone); yellow ‘wood’ on the throne, with lead-tin yellow and a little red earth, two types of glass, 10–20 µma

soda ash; high Al (sand)

11.8

2.4

5.0h

63.6

0.5

1.0

1.2

3.5

8.1

0.2

1.6

1.0

Italian

Raphael, The Madonna and Child with Saint John the Baptist and Saint Nicholas of Bari (The Ansidei Madonna) (NG 1171), 1505, Umbria or Florence.

Pale yellow priming, with lead white and a little lead-tin yellow; dark purple underside of the canopy over the throne, with red lake, a little vermilion and black; Saint John’s red drapery, with red lake; pale grey architecture, with lead white and bismuth metal powder; mordant for the gilded decoration on the throne (used alone); yellow ‘wood’ on the throne, with lead-tin yellow and a little red earth, two types of glass, 10–20 µma

soda ash; low Al (pebbles)

10.9

3.2

1.5

66.6

0.2

1.4d

0.0

2.4

10.4

0.1

1.0

0.5

Italian

Raphael, The Madonna and Child with the Infant Baptist (The Garvagh Madonna) (NG 744), c.1509–10.

Shadow of red robe of man at right, with red lake (lower glaze layers only, and not final blotted glaze), c.10–20 µma

wood ash–lime (high lime–low potash)

1.5

3.1

4.0

61.0

3.0

0.7

0.5

5.4

19.0

0.3

0.9

0.7

Spanish

Luis de Morales, The Virgin and Child (NG 1229), probably 1565–70.

Red of Virgin’s dress, with red lake and a little lead white, 5–7 µma

soda ash, some particles leached

11.5

3.5

2.3

67.5

0.5

2.7d

1.4

3.5

5.8

0.1

0.7

0.6

a. Analysis carried out on carbon-coated samples under high vacuum conditions, 200 pA, 25 kV, 60s livetime.b. Analysis carried out on uncoated samples under variable pressure conditions, 200 pA, 25 kV, 60s livetime, 50 Pa, air as the chamber gas.c. Particles that seem to be a pure form of silica, containing only small amounts of other elements, were also detected in this sample.d. The apparent elevated sulphur concentration in this sample is probably not reliable and likely to result either from a sulphur-containing red lake pigment or, due to overlap of the sulphur peak with that from lead, a contribution to the spectrum from lead pigments around the glass.e. Red lake pigments, especially those based on insect dyestuffs, often contain phosphorus. This could contribute to the apparent concentration in the glass, especially where the particles are small.f. The binding medium of many of these paintings has been analysed by Gas Chromatography–Mass Spectrometry and identified as a drying oil. These analyses have generally been published in past issues of the National Gallery Technical Bulletin.g. In this sample the glass particles are very small and are embedded in a matrix of red lake, with a substrate containing alumina. The interaction volume of the electron beam is likely to be larger than the glass particle and the apparent aluminium concentration too high.h. The quantitative results quoted are from a particle in the priming layer, which does not contain red lake, or from a large particle in red lake paint; the high reported Al content is therefore reliable.i. A dispersion of a paint sample allowed individual glass particles to be seen in transmitted light under the microscope. They could be seen to have angular edges and showed conchoidal fracture, confirming that they were glass, despite the rather low alkali content seen by EDX analysis, which is a result of severe leaching. See the Appendix in J. Dunkerton and H. Howard, ‘Sebastiano del Piombo’s Raising of Lazarus: A History of Change’, National Gallery Technical Bulletin, 30, 2009, pp. 26–51.j. Details updated after publication, 2012.